The present invention relates to a semiconductor device, and more specifically, to a fuse included in a high integrated semiconductor device for determining an electric signal transfer or an electric connection between different two terminals.
Generally, a fuse is defined as a kind of automatic cut-off device for preventing an overcurrent from flowing through an electric wire. That is, the fuse is melted due to heat generated by an overflow of electricity. Such a fuse can be easily found in common electrical appliances. The fuse allows the electric current to continuously flow at a normal level; however, once the fuse is cut, the electric current is permanently blocked unless the fuse is replaced with a new one. This point differentiates the fuse from a switch capable of controlling the flow of the electric current.
A semiconductor device is made using a number of processes including a process of doping impurities into a predetermined region within a silicon wafer and depositing new material thereon. A typical example of the semiconductor device is a semiconductor memory device. The semiconductor memory device internally includes many elements such as a transistor, a capacitor, a resistor and the like for performing a determined purpose, and the fuse is one of the elements included therein. The fuse is used in many areas within the semiconductor memory device. a redundancy circuit and a power supply circuit are typical examples of them. The fuse used in such a circuit is kept in a normal state (i.e., unblown state) during a manufacturing process. However, after the manufacturing process, the fuse can be selectively blown (i.e., cut) during a testing process.
Redundancy circuit will be explained in detail. In the case that a particular unit cell is defective in the semiconductor memory device, the defective unit cell is replaced with a redundant cell through a recovering step. That is, an address of the defective unit cell is stored at the recovering step in order to prevent the detective unit cell from being accessed. When an address of the defective unit cell is inputted externally, the redundant cell instead of the defective unit cell is activated by the redundancy circuit. The fuse of the redundancy circuit is used for storing the address of the defective unit cell at the recovering step, and the fuse coupled to the defective cell is subject to blowing by beaming a laser to that fuse so that an electrically connected point is permanently cut. This is referred as a fuse blowing.
In the case of the semiconductor memory device, a plurality of unit cells is included. After the manufacturing process, it is hard to find out how many unit cells are defective as well as where the defective unit cell exists among the plurality of unit cells. Therefore, a fuse box including a plurality of fuses is provided within the semiconductor memory device in order to replace the defective unit cells with the redundant cells.
The data storage capacity of a semiconductor memory device is increased more and more. Accordingly, the number of unit cells included in a semiconductor device each is increased and the number of fuses used for replacing defective unit cells with the redundant normal cells is also increased. On the contrary, the size of the semiconductor memory device is required to decrease for high integration. As above-mentioned, a laser is used to selectively blow out fuses. It is well known that a predetermined interval between adjacent fuses should be kept so as not to influence a neighboring fuse which is not a target of the blowing process. However, this characteristic of the fuse box is not compatible with high integration of the semiconductor memory device. Accordingly, a technology is required which is capable of preventing unselected fuses from being blown during a blowing process while keeping up the required integration.
FIGS. 1A and 1B are a plan view and a cross-sectional view for explaining a fuse included in a conventional semiconductor device.
Referring to FIG. 1A, a plurality of fuses 114 is arranged in parallel in a fuse box included in the conventional semiconductor device.
Referring to FIG. 1B, contacts 106 and 108 are formed under both ends of each fuse 114. The contacts 106 and 108 are respectively connected to different terminals to which different voltages are supplied or different circuits are connected.
In a center part of each fuse 114, a blowing region 122 is included. The blowing region 122 can be removed by beaming a laser during a blowing process in order to cut electricity between the both ends of the fuse 114.
FIGS. 2A and 2B are a cross-sectional view and a plan view for explaining operation and a problem of the fuse included in the conventional semiconductor device shown in FIG. 1.
FIG. 2A shows a normal structure after the blowing region 122 included in the fuse 114 is removed after the blowing process. If conductive material constituting the fuse 114 is completely removed, the both ends of the fuse 114 are electrically isolated from each other so that an electric charge flow between different two terminals connected through the contacts 106 and 108 is cut off.
Recently, the size and the area of a wire, a fuse and the like included in a highly integrated semiconductor device have been decreased increasing the resistance. Therefore, copper (Cu) whose resistance value is low is used as fuse material. However, copper (Cu) is soft and has high heat conductivity, and is also more corrosive compared with other commonly used metal materials. Thus, residuals generated when the fuse is blown or may migrate to adjacent areas under a high temperature condition or a high humidity condition.
Referring to FIG. 2B, even after fuse blowing process was done, at a partial fuse (114A), both ends of the fuse may still remain electrically connected due to migration of the copper (Cu). When the fuse remains connected due to copper migration even after the fuse blowing operation, the reliability of the semiconductor device may be seriously affected. Besides, migration of copper (Cu) may cause damage on a neighboring fuse which is not supposed to be blown.
For preventing the above-mentioned shortcomings such as thermal degradation and the like, metal such as aluminum, tungsten and the like whose heat conductivity is relatively low in comparison with the copper has been used for manufacturing the fuse. However, in the case of forming a fuse or a wire using these metals, high resistance of these metals cause problem at a microscopic level process, and thus a processing speed becomes slow or power loss may occur due to leakage current. To overcome this problem, the size of the fuse or the wire should be increased. However, this solution is not compatible with high integration of the semiconductor device. Alternatively, as above-mentioned, in the case of forming the fuse using the copper, the fuse formation is difficult due to the properties of the copper. Therefore, a new fuse which is suitable for a high integrated semiconductor memory device is required.